1. Field of the Art
The present invention relates to a solenoid-operated hydraulic control device for an anti-skid brake system for a vehicle, to directly or indirectly control a pressure of a fluid in a brake cylinder.
2. Related Art Statement
An anti-skid hydraulic brake system for a vehicle is known. For example, Japanese Patent Application laid open in 1983 under Publication No. 58-224839, discloses an anti-skid device of indirect pressure control type wherein a pressure of a brake fluid in a brake cylinder is indirectly controlled by a pressure regulator which is operated by a fluid delivered from a pressure source which is different from a pressure source for the brake cylinder. Further, Japanese Patent Application laid open in 1981 under Publication No. 56-142733 discloses an anti-skid device of direct pressure control type wherein a solenoid-operated hydraulic control device is disposed in a primary fluid passage which connects a master cylinder and a brake cylinder.
A solenoid-operated hydraulic control device is provided to control a pressure of a fluid in a pressure chamber of a hydraulically operated actuator, for example, a pressure regulator when the control device is used in an anti-skid device of indirect pressure control type, or a brake cylinder when the control device is used in an anti-skid device of direct pressure control type.
An example of the solenoid-operated hydraulic control device consists of a combination of a solenoid-operated directional control valve and a solenoid-operated flow control valve. The directional control valve is electromagnetically operated between a first position for communication of the pressure chamber in the hydraulic actuator with a hydraulic power source such as a master cylinder or a pump, and a second position for communication of the pressure chamber in the actuator with a reservoir. The fluid from the pressure source may be fed into the hydraulic actuator when the directional control valve is placed in the first position. In the second position, the fluid in the hydraulic actuator may be discharged into the reservoir. The flow control valve is disposed between the directional control valve and the hydraulic actuator whose pressure is controlled by the hydraulic control device. The flow control valve has a restrictor passage for restricting a flow of the fluid through the valve, and a non-restrictor passage formed in parallel with the restrictor passage. The flow control valve is electromagnetically operated between a non-restricting position in which the fluid flows through both of the restrictor passage and the non-restrictor passage, and a flow-restricting position in which the non-restrictor passage is closed and the fluid is forced to flow through the restrictor passage. Thus, the flow control device is capable of controlling a rate of flow of the fluid therethrough in two steps.
The abovementioned solenoid-operated hydraulic control device consisting of the solenoid-operated directional control and flow control valves is capable of effecting a pressure regulating operation in four modes which permit a rapid rise, a rapid fall, a slow rise and a slow fall, respectively, of the pressure in the hydraulic actuator. Thus, the pressure in the hydraulic actuator may be suitably regulated so as to be held within an optimum range.